Observing the Stars of Perseus

The Winter Constellation of Soldier with Sword

The constellation Perseus has much to offer in the winter sky, lying on the Milky Way.

Locating the Constellation Perseus

Perseus is not too hard to find. It rises in the northeast after sunset in fall and is up high in the sky all winter. Look below the W shape of Cassiopeia toward the horizon. A string of stars seems to dangle from the left edge of the W shape. This string of stars is Perseus.

Perseus can also be found not far from the star cluster of the Pleiades. In fact, as the string of stars drops downward, it appears to point right to that tiny, well-known cluster.

Perseus is called the Soldier with Sword. The ancients saw a great warrior here who slew the evil Medusa. He is said to be carrying her severed head in one hand and his sword in the other. Perseus rode the nearby Pegasus when he went to rescue Andromeda from the sea monster.

The Stars of Perseus

The brightest star in Perseus is near the center of the constellation. Alpha Persei, or Mirfak, shines at magnitude 1.79. It lies about 592 light-years away. Almost 10 degrees to Mirfak’s right is the second brightest star, Algol. Algol shines at magnitude 2.09 and represents the head of Medusa. Algol’s nickname is The Demon Star (The Ghoul) because it is an eclipsing binary. It changes in brightness as the two stars orbit each other, approximately every 69 hours. This results in a “blinking” of the star as it dims for about four hours at a time.

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A number of the stars that make up the dangling stick form of Perseus are around the 3rd magnitude. Starting above Mirfak you’ll find Gamma Persei; below Mirfak is Delta Persei; below that is Epsilon Persei, and at the bottom, closest to the Pleiades is Zeta Persei or Atik.

Messier and NGC Objects in the Soldier with Sword

The most popular deep-sky target in this constellation is not a Messier object but the Double Cluster in Perseus, NGC 869 and NGC 884. At a bright magnitude 4.0, it is easy to locate and shows up nicely in binoculars. The Double Cluster lies just above the “stick” of stars that make up Perseus’s body. In the Northern Hemisphere, this grouping is always above the horizon, making it a popular target for observing year-round. These young stars lie about 7000 light-years from Earth and only a couple hundred light-years from each other.

About seven degrees to the right of the Double Cluster and below the left V in the W-shape of Cassiopeia is M76, or the Little Dumbbell. This planetary nebula is a dim magnitude 12.0 but is also always above the horizon for northern observers.

Thirteen degrees below M76 and not far from Algol is the other Messier object in Perseus, M34. This open cluster shines at magnitude 5.2, an easy catch in binoculars.

The last well-known target in Perseus lies on the stick figure between the bottom two 3rd magnitude stars, Epsilon Persei and Zeta Persei (Atik). It is NGC 1499, or the California Nebula. Although under perfect conditions its light can be glimpsed without optical aid, it is not much of a target for telescopes because of its low surface brightness. The fame of this object comes from beautiful astrophotos, and yes it does look a bit like California.

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To learn more about observing the constellations, read the classic three-volume set of Burnham’s Celestial Handbook by Robert Burnham.

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